[RESOLVED] Unable to Re-instal back Wndows XP ?

[slickcondo]

Please help ! I have a odd problem. Current status:

Fujitsu T2010 32bit
No CD Rom drives
HDD 500GB installed a few months ago
Came installed with Windows Vista
Subsequent upgraded to Windows 7 and over a month ago,
Windows Update prompted upgrade to Windows 10 and done successfully.
Now unable to roll back to Windows7 as upgrade is over a month ago.
Reason wishing to roll back...new Windows 10 too unproductive as too much new things to learn and not getting on with what I wanted to do with my work. Gotten used to XP after so many years using it even though its no longer supported by MS.

Today:
Tried to installed Windows XP from my Windows XP with SP3 DVD disk using a external USB DVD Rom drive attached.
On bootup, after downloading Windows Setup program from the DVD disk, it says no drives detected
Option to install 1) external drive by pressing S or
2) Press Enter to continue.

Pressing S gave few options of external hard drive brands (I think). Choose Others as my LiteOn USB hard drive option is not given on the list.
It says cannot continue because no Hard Drive detected.

Tried installing Windows XP on USB Flash drive. After boot up, it says C drive partition have 978MB of MBR and too small for Windows XP
Tried to delete the partition. After deleted, Unpartitioned drive about same capacity - about 978MB or a little more. Stil insufficient space to install Win XP
But HDD is 500GB and only have Win10 operating systems on it.
So cannot continue with XP installation.

Any reason why this happens and how to overcome it ? Any questions please don't hesitate to ask. Thanks